Performing a tune up for a friend. 1992 500SL. Runs reasonably well off idle but idles rough. Did notice upon getting it to my shop that it is very low on fuel, not good. Guessing new plugs, wires, caps, rotors, filters. Anything else I might consider as this thing has sat for a while. Do I need to buy the high dollar o.e.m. stuff or is the locally available stuff good enough? ie. Bosch vs Carquest. I've seen the tune up kits available for just over $500. Besides the tune up it has a non-working driver side window and a convertible top that only begins to retract and then stops. Any advice would be greatly appreciated. First time working on a Mercedes! I do own an '89 Jaguar XJS V12 so the Mercedes isn't as imposing.